This invention relates to material handling apparatus and more particularly to a pallet molded of synthetic resin material or the like adapted to form part of a container for transporting, supporting, and storing a load of fine granular, particulate, powdered or other fluidizable material, and for fluidized unloading of the load from the container.
The pallet of this invention represents an improvement over the container disclosed in the coassigned U.S. Pat. No. 4,007,694, and commercially available from the assignee of this invention, Semi-Bulk Systems, Inc. of St. Louis, Mo. under their registered trademark AIR PALLET. The pallet disclosed in the above-noted patent is generally circular, as viewed from above, having a number of legs spaced for the entrance of the tines of a forklift from any of four directions. The pallet has a peripheral wall extending around the pallet and an upwardly facing deck supported by the peripheral wall for supporting the load. The deck slopes downwardly toward one side of the pallet and is adapted to have a porous diaphragm of cloth or the like secured thereto with the diaphragm covering the deck. An outlet opening is provided in the peripheral wall of this prior art pallet above the level of the deck at the lowest side thereof through which the powdered load may be discharged or unloaded. An inlet opening also extends through the peripheral wall for introducing compressed air into the space between the diaphragm and the deck. The compressed air flows upwardly through the porous diaphragm for fluidizing the powdered load bearing against the diaphragm.
The prior art container described in the above-mentioned patent had a tubular plastic film bag secured to its pallet. This bag was generally of the same diameter as the pallet (e.g., about 42 inches in diameter) and was of sufficient height to contain a desired quantity of powder (e.g., 500-4,000 pounds or more). The bag was typically attached to the peripheral wall of the pallet by means of a metal strap band on the outside of the bottom of the bag, tightened therearound and secured in place. Typically, this strapping band was of the well known type (nylon) used to band shipping containers commercially available from Signode Corporation of Chicago, Ill. and other companies. Upon pressurizing the interior of the bag during fluidized unloading of the load, the air pressure would, on occasion, pull the bag from between the strap and the pallet with the resultant loss of fluidization air and spillage of the powdered load. Although this rarely occurred, it was a serious problem when it did occur because the escaping powder often prevented resealing of the bag to the pallet and thus the load could not be fluidized for unloading and would continue spilling from the container. It was also recognized that because the pallet was preferably molded of synthetic resin material, it suffered from some degree of inherent dimensional instability and it would relax when a strap was tightly applied therearound.